GCSE Electronics: Oscilloscope and Sound Waves

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Questions and Answers

What is the reason why a sound wave appears strange when displayed on an oscilloscope?

It is made up of waves of many different frequencies added together (correct)

It is a type of sine wave

It is a type of DC signal

It is made up of waves of a single frequency

What is the definition of amplitude of a wave?

The minimum 'height' of the negative part of a wave

The frequency of a wave

The maximum 'height' of the positive part of a wave (correct)

The average 'height' of a wave

What type of waveform is often used to study the operation of a basic amplifier system?

Square wave

Sine wave (correct)

Sawtooth wave

Triangle wave

What is the main difference between the waveforms of different musical instruments?

Their range of frequencies Signup and view all the answers

What is the purpose of using an oscilloscope in the study of sound waves?

To display the waveform of the sound wave Signup and view all the answers

What is a characteristic of a sound wave displayed on an oscilloscope?

It is made up of many simple waves added together Signup and view all the answers

What can be said about the waveforms of different musical instruments playing the same note?

They look completely different Signup and view all the answers

What is the main characteristic of an AC signal?

It has both positive and negative voltages Signup and view all the answers

What is the primary function of an amplifier in a signal processing system?

To boost the amplitude of the signal while keeping the frequency unchanged Signup and view all the answers

What is the range of frequencies that a telephone amplifier is designed to accept?

300 Hz to 3 kHz Signup and view all the answers

What would happen if a video signal with frequencies as high as 6 MHz is passed through an audio amplifier designed for frequencies up to 20 kHz?

The amplifier would not obtain the correct output Signup and view all the answers

What is the bandwidth of an amplifier defined as?

The range of frequencies that can be amplified to more than 70% of the maximum gain Signup and view all the answers

What is the significance of the 70% mark in the amplifier's frequency response?

It is the point where half the original signal power is lost Signup and view all the answers

Why is it difficult to design an amplifier to cover the entire frequency range?

Because amplifiers contain components that respond differently to different frequencies Signup and view all the answers

What is the purpose of specifying the bandwidth of an amplifier?

To determine the range of frequencies that can be amplified correctly Signup and view all the answers

What is the frequency range of a music amplifier?

20 Hz to 20 kHz Signup and view all the answers

What is the purpose of Step 1 in the frequency response problem?

To find 70% of the maximum gain of the amplifier Signup and view all the answers

What is the method used to estimate the bandwidth of the amplifier?

By finding 70% of the maximum gain and then finding the corresponding frequency Signup and view all the answers

What is the unit of the bandwidth read off from the frequency axis?

kHz Signup and view all the answers

What is the voltage gain of the pre-amplifier in Example 2?

200 Signup and view all the answers

What is the purpose of the red line drawn in Step 2 of the frequency response problem?

To show 70% of the maximum gain of the amplifier Signup and view all the answers

What is the bandwidth of the amplifier in Example 1?

25 kHz Signup and view all the answers

What is the method used to sketch the frequency response of the pre-amplifier in Example 2?

By drawing a graph with the given voltage gain and bandwidth Signup and view all the answers

What is the purpose of the blue line drawn in Step 3 of the frequency response problem?

To find the frequency at which the gain is 70% of the maximum gain Signup and view all the answers

If an amplifier has a bandwidth of 5 kHz when the gain is 10, what will be the bandwidth when the gain is increased to 50?

1 kHz Signup and view all the answers

What is the relationship between gain and bandwidth in an amplifier?

As gain increases, bandwidth decreases Signup and view all the answers

If an amplifier has a bandwidth of 20 kHz when the gain is 5, what will be the bandwidth when the gain is increased to 10?

4 kHz Signup and view all the answers

What is the bandwidth of an amplifier with a gain of 200 and a gain-bandwidth product of 1 MHz?

5 kHz Signup and view all the answers

What is the gain-bandwidth product of an amplifier with a gain of 50 and a bandwidth of 20 kHz?

1 MHz Signup and view all the answers

If an amplifier has a bandwidth of 10 kHz when the gain is 20, what will be the gain when the bandwidth is decreased to 5 kHz?

40 Signup and view all the answers

What is the voltage gain of an amplifier with a frequency response as shown in the graph?

300 Signup and view all the answers

How is the bandwidth of an amplifier related to its frequency response graph?

The bandwidth is the frequency range at which the voltage gain is above 0.707 Signup and view all the answers

What is the relationship between the voltage gain and bandwidth of an amplifier?

The higher the voltage gain, the smaller its bandwidth. Signup and view all the answers

What is the point at which the gain of an amplifier is 70% of its maximum gain?

At the maximum bandwidth Signup and view all the answers

What is the gain-bandwidth product of an amplifier that has a gain of 10 and a bandwidth of 100 kHz?

1 MHz Signup and view all the answers

What happens to the gain of an amplifier as the frequency increases?

The gain decreases Signup and view all the answers

What is the maximum gain of an amplifier in the given graph?

200 Signup and view all the answers

What is the frequency at which the gain of an amplifier is 70% of its maximum gain?

20 kHz Signup and view all the answers

What is the relationship between the gain and bandwidth of an amplifier with a gain-bandwidth product of 1 MHz?

The gain is inversely proportional to the bandwidth Signup and view all the answers

What is the purpose of the gain-bandwidth product in an amplifier?

To describe the relationship between the gain and bandwidth of an amplifier Signup and view all the answers

Study Notes

Voltage Gain and Bandwidth

The voltage gain of an amplifier is closely linked to its bandwidth, with a higher voltage gain resulting in a smaller bandwidth. This is because a higher gain indicates a more selective amplification, which rejects signals outside of the desired frequency range, thereby reducing the bandwidth.
The gain-bandwidth product is a key concept, where the product of the gain and bandwidth is constant for a given amplifier. This means that if the gain of an amplifier is increased, its bandwidth will decrease, and vice versa. This concept is crucial in the design of amplifiers, as it allows engineers to optimize the trade-off between gain and bandwidth.

Graph of Voltage Gain vs Frequency

The graph of voltage gain vs frequency shows a decrease in gain from the maximum gain, with the bandwidth being the range of frequencies that can be amplified to more than 70% of the maximum gain. This graph provides a visual representation of the gain-bandwidth trade-off, allowing designers to easily identify the optimal operating point for their amplifier.
The graph can be used to estimate the bandwidth of an amplifier by drawing a horizontal line at 70% of the maximum gain and reading off the frequency at which the line intersects with the graph. This method provides a quick and accurate way to determine the bandwidth of an amplifier, without requiring complex calculations or simulations.

Examples of Voltage Gain and Bandwidth

Example 1: An amplifier has a maximum gain of 400 and a bandwidth of 25 kHz when the gain is 280. In this example, the amplifier is designed to operate at a gain of 280, which corresponds to a bandwidth of 25 kHz. This means that the amplifier is capable of amplifying frequencies up to 25 kHz with an amplitude of at least 70% of the maximum gain.
Example 2: A pre-amplifier with a voltage gain of 200 has a bandwidth of 20 kHz, and the gain x bandwidth product is 1 MHz. In this example, the pre-amplifier is designed to operate at a gain of 200, which corresponds to a bandwidth of 20 kHz. Additionally, the product of the gain and bandwidth is 1 MHz, indicating that the amplifier is capable of amplifying signals up to 1 MHz.

Amplitude and Frequency of AC Signals

An AC signal contains both positive and negative voltages, and its amplitude is defined as the maximum 'height' of the positive part of the wave. The amplitude of an AC signal determines the magnitude of the voltage variation, and is a critical parameter in the design of amplifiers.
The frequency of an AC signal can also change, and amplifiers must boost the amplitude of the signal while leaving the frequency unchanged. This means that amplifiers must be designed to operate over a specific range of frequencies, and must be able to handle signals with varying amplitudes and frequencies.

Designing Amplifiers

Amplifiers are designed to accept a specific range of frequencies, and the range of frequencies that can be amplified correctly is defined as the bandwidth of the amplifier. To design an amplifier, engineers must consider the desired frequency range, the gain required, and the noise and distortion limits.
Different amplifiers are designed for different frequency ranges, such as telephone amplifiers (300 Hz to 3 kHz) and music amplifiers (20 Hz to 20 kHz). Each amplifier is optimized for its specific application, taking into account the characteristics of the signals to be amplified.

Exercise 5.3

Exercise 5.3 provides practice questions for calculating the bandwidth of an amplifier based on its gain and gain-bandwidth product. These questions allow students to apply the concepts learned in this section to real-world problems, and to develop a deeper understanding of the relationship between gain, bandwidth, and frequency response.

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Description

This quiz is about using an oscilloscope to visualize sound waves by connecting it to a microphone. It demonstrates how the oscilloscope shows a waveform that changes as you talk.